The research goal is to elucidate a transcriptional cascade involved in mesodermal patterning and development in the nematode Caenorhabditis elegans. The hypothesis that two basic helix-loop-helix transcription factors, CeTwist and CeE/DA, together activate target genes that affect mesodermal fate and function will be tested. Specific Aim 1 will investigate the genetic interactions of CeTwist, CeE/DA, and unknown proteins at target promoters by performing a genetic screen designed to find suppressors of a special allele of the CeTwist gene. In Specific Aim 2, DNA microarrays will be hybridized with RNA made from animals overexpressing CeTwist and CeEDA to identify downstream target genes which will be subsequently characterized. These studies are medically relevant because individuals with mutations in the human Twist gene are afflicted with Saethre-Chotzen syndrome. This syndrome is characterized by the premature fusion of cranial sutures called craniosynostosis. Similar defects are found in other syndromes associated with downstream Twist target genes that have homologs in C elegans. Out of about 100 related forms of craniosynostosis, 30 are thought to arise from single gene disorders, and a specific gene has been identified in less than 10 disorders. New genes in the pathway that are identified in C elegans are predicted to be good candidates for the unknown genetic basis underlying these human disorders.